The present invention is directed toward mechanical and/or chemical-mechanical planarization of microelectronic-device substrate assemblies. More specifically, the invention is related to planarizing machines and methods for selectively using abrasive slurries on fixed-abrasive planarizing pads.
Mechanical and chemical-mechanical planarizing processes (collectively xe2x80x9cCMPxe2x80x9d) remove material from the surface of semiconductor wafers, field emission displays or other microelectronic substrates in the production of microelectronic devices and other products. FIG. 1 schematically illustrates a CMP machine 10 with a platen 20, a carrier assembly 30, and a planarizing pad 40. The CMP machine 10 may also have an under-pad 25 attached to an upper surface 22 of the platen 20 and the lower surface of the planarizing pad 40. A drive assembly 26 rotates the platen 20 (indicated by arrow F), or it reciprocates the platen 20 back and forth (indicated by arrow G). Since the planarizing pad 40 is attached to the under-pad 25, the planarizing pad 40 moves with the platen 20 during planarization.
The carrier assembly 30 has a head 32 to which a substrate 12 may be attached, or the substrate 12 may be attached to a resilient pad 34 in the head 32. The head 32 may be a free-floating wafer carrier, or an actuator assembly 36 may be coupled to the head 32 to impart axial and/or rotational motion to the substrate 12 (indicated by arrows H and I, respectively).
The planarizing pad 40 and a planarizing solution 44 on the pad 40 collectively define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate 12. The planarizing pad 40 can be a fixed-abrasive planarizing pad in which abrasive particles are fixedly bonded to a suspension material. In fixed-abrasive applications, the planarizing solution 44 is typically a non-abrasive xe2x80x9cclean solutionxe2x80x9d without abrasive particles. In other applications, the planarizing pad 40 can be a non-abrasive pad composed of a polymeric material (e.g., polyurethane), resin, felt or other suitable materials. The planarizing solutions 44 used with the non-abrasive planarizing pads are typically abrasive slurries with abrasive particles suspended in a liquid.
To planarize the substrate 12 with the CMP machine 10, the carrier assembly 30 presses the substrate 12 face-downward against the polishing medium. More specifically, the carrier assembly 30 generally presses the substrate 12 against the planarizing liquid 44 on a planarizing surface 42 of the planarizing pad 40, and the platen 20 and/or the carrier assembly 30 move to rub the substrate 12 against the planarizing surface 42. As the substrate 12 rubs against the planarizing surface 42, material is removed from the face of the substrate 12.
CMP processes should consistently and accurately produce a uniformly planar surface on the substrate to enable precise fabrication of circuits and photo-patterns. During the construction of transistors, contacts, interconnects and other features, many substrates develop large xe2x80x9cstep heightsxe2x80x9d that create highly topographic surfaces. Such highly topographical surfaces can impair the accuracy of subsequent photolithographic procedures and other processes that are necessary for forming sub-micron features. For example, it is difficult to accurately focus photo patterns to within tolerances approaching 0.1 micron on topographic surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical surface into a highly uniform, planar surface at various stages of manufacturing microelectronic devices on a substrate.
In the highly competitive semiconductor industry, it is also desirable to maximize the throughput of CMP processing by producing a planar surface on a substrate as quickly as possible. The throughput of CMP processing is a function, at least in part, of the polishing rate of the substrate assembly and the ability to accurately stop CMP processing at a desired endpoint. Therefore, it is generally desirable for CMP processes to provide (a) a uniform polishing rate across the face of a substrate to enhance the planarity of the finished substrate surface, and (b) a reasonably consistent polishing rate during a planarizing cycle to enhance the accuracy of determining the endpoint of a planarizing cycle.
Although fixed-abrasive planarizing pads have several advantages compared to non-abrasive pads, fixed-abrasive pads may not produce consistent polishing rates throughout a planarizing cycle. One drawback of fixed-abrasive pads is that the polishing rate may be unexpectedly low at the beginning of a planarizing cycle. The inconsistency of the polishing rate for fixed-abrasive pads is not completely understood, but when a non-abrasive planarizing solution is used on a fixed-abrasive pad, the polishing rate of a topographical surface starts out low and then increases during an initial stage of a planarizing cycle. Such an increase in the polishing rate of a topographical substrate is unexpected because the polishing rate of a topographical substrate on a non-abrasive pad with an abrasive slurry generally decreases during the initial stage of a planarizing cycle. Therefore, it would be desirable to increase the consistency of the polishing rate on fixed-abrasive pads.
Another drawback of fixed-abrasive pads is that the polishing rate is low when planarizing a blanket surface (e.g., a planar surface that is not yet at the endpoint). The polishing rate of blanket surfaces is also relatively low on non-abrasive pads, but the polishing rate of such surfaces is generally even lower on fixed-abrasive pads. Therefore, it would be desirable to increase the polishing rate of blanket surfaces when using fixed-abrasive pads.
The present invention is directed toward planarizing machines and methods for selectively using abrasive slurries on fixed-abrasive planarizing pads in mechanical and/or chemical-mechanical planarization of microelectronic substrate assemblies. In one embodiment of a method in accordance with the invention, a microelectronic substrate is planarized by positioning a fixed-abrasive planarizing pad on a table of a planarizing machine, covering at least a portion of a planarizing surface on the pad with a first abrasive planarizing solution during a first stage of a planarizing cycle, and then adjusting a concentration of the abrasive particles on the planarizing surface at a second stage of the planarizing cycle. The fixed-abrasive pad can include a planarizing medium comprising a binder and a plurality of first abrasive particles fixedly attached to the binder so that at least a share of the first abrasive particles are exposed at the planarizing surface. The first abrasive planarizing solution has a plurality of second abrasive particles that are distributed across at least a portion of the planarizing surface during the first stage of the planarizing cycle. The first abrasive planarizing solution and the fixed-abrasive pad operate together to remove material from the microelectronic substrate. For example, material can be removed from the microelectronic substrate by rubbing the substrate against the first abrasive particles at the planarizing surface and the second abrasive particle suspended in the first planarizing solution.
The concentration of the second abrasive particles on the planarizing surface can be adjusted during the second stage of the planarizing cycle by a number of different procedures. In one embodiment, the planarizing surface is coated with a second non-abrasive second planarizing solution without abrasive particles during the second stage of the planarizing cycle to reduce the concentration of the second abrasive particles on the planarizing surface. The second planarizing solution can be dispensed onto the planarizing surface after terminating a flow of the first planarizing solution at the end of the first stage of the planarizing cycle. In another embodiment, the flow of the first planarizing solution can be continued after the first stage of the planarizing cycle, and a flow of the second planarizing solution can be combined with the first planarizing solution during the second stage so that a combined flow of the first and second planarizing solutions is dispensed onto the polishing pad. The methods accordingly use the abrasive first planarizing solution during a pre-wetting or initial phase of the planarizing cycle, and then they use either only the second planarizing solution or a combination of the first and second planarizing solutions during a subsequent phase the second stage of the planarizing cycle.